Automatic headlight dimmer system



Dec. 20, 1960 M. WOODWARD ET AL 2,965,813

/ AUTOMATIC HEADLIGHT DIMMER SYSTEM Filed Oct. 26, 1954 M w mflw m M If y A w w United States Patent 2,965,813 AUTOMATIC HEADLIGHT DIMMER SYSTEM Myrneth L. Woodward, Harold E. Todd, and George W. Onksen, Anderson, Ind., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Oct. 26, 1954, Ser. No. 464,834 3 Claims. (til. 317-130) This invention relates to light sensitive switching means and, more particularly, to light sensitive switching means used for switching between filaments in multifilament automotive headlamps to automatically dim the same.

In some of the current automatic headlamp dimming systems a photomultiplier tube is used for actuating the control circuit, since it is a very sensitive and powerful device and provides a considerable amount of output for control purposes. However, these tubes require a relatively high voltage for actuation and, therefore, a special power supply unit which is expensive.

It is an object in making the present invention to provide a light control circuit utilizing a photomultiplier tube in which the voltage supplied to the tube is reduced from that previously used.

It is a further object in making this invention to provide various modifications assisting in obtaining maximum output from the various components of the system to compensate for operation at a lower voltage.

It is a still further object in making this invention to provide a very efficient light sensitive control system in obtaining a maximum output from the components used.

With these and other objects in view which will become apparent as the specification proceeds, our invention will be best understood by reference to the following specification and claims and the illustrations in the drawing, in which:

The figure is a circuit diagram of a light sensitive control system embodying our invention. Referring now more particularly to the drawing, the light sensitive systern consists in general of two main units, one a light sensitive pickup unit indicated at 2 which is mounted at some point in the vehicle so that incident light from the front of the vehicle may be concentrated therein and, second, an amplifier unit 4 connected thereto by conductors which may be mounted at any other suitable location in the car. The light sensitive unit 2 consists of a photomultiplier tube 6 which may be one commercially on the market at the present time and consists of a cathode 8, an anode 10, and a series of multiplying dynodes 12. This tube serves both as a light sensitive pickup and as an amplifying means. The cathode and dynodes are supplied with power from an incoming conductor 14 which is connected to one end of a plurality of series resistors 16 which provide sequential drops in voltage between the cathode and each of the dynodes to ground in sequence so that each has a progressively lower voltage. The dynodes each are connected at points between two of the resistors 16 through a limiting resistor 18 which limits the current flow in any one dynode circuit to protect the tube from burning out when an excessive amount of light falls thereon. The anode 10 is connected back to the amplifying unit 4 through conductor 26. Thus, if the amount of light falling on the photomultiplier tube 6 varies, the current flow through the conductor 2a varies in proportion and provides a control signal. The photomultiplier is, of course, mounted in suitable means to concentrate the light properly thereon.

The main power for the unit is supplied from the vehicle battery B which is connected to conductor 1% through control switch 1. However, since this is a low voltage supply, either 6 volt or 12 volt depending upon the type of car, this is, of course, insuilicient to provide ice the high voltage necessary in other parts of the circuit. A power supply unit is, therefore, provided which consists of a mechanical vibrator 24 for interrupting the DC. current which Vibrator is connected to the primary 26 of a transformer having a plurality of secondaries, one a high voltage secondary 2S and the second a lower voltage secondary 30. The vibrator consists of two spaced stationary contacts 32 and 34, contact 32 being connected to one terminal of the primary 26 and contact 34 to the other side of the primary 26. An oscillating reed or armature 36 is adapted to vibrate between the two stationary contacts 32 and 34 and is connected to ground. A small operating coil 38 has one terminal connected to stationary contact 34 and the other terminal connected to ground. This coil, therefore, is energized to attract armature '36 and move the same into engagement with stationary contact 34 at which time the coil is shorted and releases the armature 36 so that it may move away from the stationary contact 34 due to spring bias and into engagement with stationary contact 32. Thus, the coil 38 is energized for approximately one-half of the time and deenergized for the remainder.

The low voltage supply conductor 22 which is connected to supply line 106 through connector 50 is connected through a ballast tube 40 to conductor 42 which extends to a center tap on primary 26. This, therefore, provides an energizing voltage alternately to the opposite halves of the primary when the armature is vibrating and thus provides a transformable power. A resistor 44 in series with an adjustable potentiometer 46 are connected between conductor 42 and ground. This provides means for adjusting the DC. voltage applied to the transformer primary. The high voltage secondary winding 28 is used to supply power to the photomultiplier tube 6 and therefore has one terminal connected through conductor 4-8 to a terminal block 50 in which conductor 48 is connected to conductor 14. Two resistances 52 and 54 are connected in series across the secondary winding 28. An adjustable tap 56 can be moved over the second resistor 54 to adjust the voltage on conductor 48 and the tap is grounded. Thus, suitable adjustable voltage is provided to the photomultiplier.

The output of the photomultiplier tube, as before mentioned, is connected through conductor 20 to the terminal block 50 where it joins with conductor 58 which extends to the control grid 60 of one section of an amplifying tube 62. This tube is shown as being a twin-triode tube but, of course, may be replaced by two separate tn'ode tubes if desired. The first tn'ode section is used as an amplifier for the output of a photomultiplier tube and this tube controls a sensitive relay 64. This relay consists of an operating coil 66, two spaced stationaiy contacts 68 and 70, and a movable armature 72 which is spring-biased toward the right into engagement with stationary contact 68 but can be moved to the left into engagement with stationary contact 70 when the current flow through operating coil 66 is suflicient to overcome this spring-bias. One terminal of the coil 66 is connected directly to plate 74 of the first triode section through conductor 76. The opposite terminal of the energizing coil 66 is connected to one side of the secondary 30 through conductor 78. The opposite side of secondary 30 is grounded and a condenser is connected directly across said secondary 30. A second condenser 82 is connected directly across energizingcoil 66.

The cathode 84 of the first section of the tube 62 is grounded. A biasing resistor 86 is connected between conductor 58 and ground. A variable resistor or potentiometer 88 is connected between conductor 58 and the stationary contact 70 of the sensitive relay 64. A small condenser 90 is likewise connected between conductor 53 and ground. These last components provide a biasing voltage for the control grid 60 which can be adjusted and varied at different portions of the operating cycle. The heater 92 of the first section of the tube 62 has one side connected to ground and the opposite side connected through a dropping resistor 94 to the supply conductor 22. A condenser 96 is connetced between conductor 22 and ground.

The second section of the tube 62 is used as a rectify" ing diode, since the grid 98 and the cathode 100 are connected together and to conductor 102 extending to the junction block 50. The plate 104 of the second section is connected to conductor 76 and, therefore, to the energizing coil 66 of the sensitive relay. This section of the tube is used to provide an override control which will be explained later. Conductor 22 is connected to junction block 50 where it is joined by incoming conductor 106 which is actually connected to the battery of the vehicle through control switch 1. A resistor 108 is connected between conductor 22 and conductor 110 which extends from stationary contact 68 of the sensitive relay 64 to the junction block 50 where it is joined to conductor 112 which runs to stationary contact 114 of the standard foot dimmer switch 126 of an automotive vehicle. The foot dimmer switch has a movable contact 116 which is connected through conductor 118 to the operating coil 120 of a power relay 122. The opposite terminal of the coil 120 is connected through line 121 to line 106. The second stationary contact 124 of the foot dimmer switch is connected directly to ground.

The power relay 122 is the device which actually switches the control circuit between upper beam and lower beam encrgization. This relay is provided with a stationary contact 128 which is connected directly to the upper beam filaments of the headlamps indicated as UB. The relay also has a second spaced stationary contact 130 which is connected directly to the lower beam filaments indicated as LB. Between these two stationary contacts a movable armature 132 is provided which is connected through lines 121, 106 and switch 1 to battery B. Thus, when armature 132 engages stationary contact 128, the upper filaments will be energized and, when it moves into engagement with stationary contact 130, the lower beam filaments will be energized. The operating coil 120 is adapted to move the armature 132 downwardly or into engagement with stationary contact 130 when it is energized and releases it to a spring-bias in an upward direction when insufficient current flows through coil 120. The override control includes conductor 102 which extends to the junction block 50 and is joined to conductor 134 therein which latter conductor extends to a stationary contact 136 of an auxiliary foot switch or override switch 138. The movable armature 140 of said switch is grounded to complete an override circuit.

The two conductors 14 and 20 that extend between the light sensitive pickup unit 2 and the junction block 50 in the amplifier unit 4 are shielded in a novel manner to prevent inductive reaction between the two. In these conductors disconnection plugs 142 and 144 are provided so that the connections may be taken apart and in conductor 20 a metal shielding 146 is provided which extends from the junction block 50 to the plug 142. In like manner, a shield 148 is provided which extends from the potentiometer formed of the resistors 16 and to plug 144 to shield conductor 14. It is to be noted that there is an overlap of the two lengths of shielding but that there are unshielded lengths in each conductor. However, by providing the overlap and the shielding of only one conductor over most of the total distance, suificient shielding is provided to prevent inductive reactance between the two conductors and yet save the cost of an in-line shielded connector.

In the supply line to the photomultiplier tube 6 it is to be noted that the secondary 28 does not have one terminal connected to ground but that the ground connection is somewhere along the potentiometer 54 depending upon 4 the setting of tap 56. Thus, there is a proportional balancing voltage above and below ground. The potentiometer, therefore, operates at a lower potential than it would if it were connected directly to the power conductor 48. Also, the voltage stress on the secondary winding is reduced by this type of connection and less opportunity for voltage breakdown will occur.

Since it is necessary to assure that the voltage applied to the photomultiplier tube 6 will never exceed a predetermined amount, care must be taken to prevent momentary surges. Since the ballast tube 40 has a low resistance when cold in starting, a considerably higher current flow occurs initially when a control switch is closed than during normal operation. In order to prevent this initial surge from applying a peak voltage which is too great to the photomultiplier tube, a circuit has been provided which absorbs the extra current but which changes as heat is available to compensate. This compensating circuit includes the heater element 150 of the second section of the tube 62. This heater element has a relatively low resistance when cold which resistance increases as the element is heated. The heater element is connected through conductor 152 to the regulated low voltage power conductor 42 and drains off the excess current which flows through the ballast tube 40 when the same is cold but as its resistance increases does not conduct or drain oil an appreciable amount of current after the element 150 and the ballast tube 40 heat up. This compensating circuit, therefore, takes care of the initial surge in starting the system.

The operation of the system is as follows. When the control switch 1 in the power conductor 106 is initially closed, power is supplied to the vibrator power pack through conductor 106, junction block 50, conductor 22, ballast tube 40, conductor 42 to the center tap of the primary 26. Through the vibrator action of vibrator 24, alternating current is supplied to the primary winding which is transformed and induces desired alternating current voltages in the secondaries 28 and 30. The voltage applied to conductor 48 may be adjusted by moving the tap 56 on potentiometer 54 and, in instances where photomultiplier tubes have previously been used and 900 volts was needed for the photomultiplier tube, the present circuit will operate satisfactorily at 700 volts on this line. It is to be noted in this circuit A.C. current is supplied directly to the photomultiplier tube. Since A.C. is used, it must be properly phased between that applied to the photomultiplier and that applied to the amplifier tube 62 and the circuit is so designed that the two are out of phase. In other words, when conductor 48 is negative, plates 74 and 104 of the amplifier tube 62 are positive. In this design, as previously mentioned, the vibrator operating coil 38 is in circuit during one-half cycle and deenergized during the other half cycle. Since only onehalf cycle is used in the photomultiplier unit, the system is so connected that the half cycle used by the photomultiplier tube is that during which the operating coil 38 is inactive, thus taking advantage of the slightly higher voltage since no loss in the coil 38 occurs during that half cycle.

The secondary 30 supplies a lower voltage to the amphfier tube 62 and to the sensitive relay 64 which controls the power relay 122. After the device has heated up and the proper voltages have been applied to the components, if no light is falling on the photomultiplier tube 6, for example when the car is being operated in rural sections or with no approaching traflic, the current output from the photomultiplier tube will be relatively small and the grid 60 of the first section of the tube 62 at a sufficiently high voltage to permit conduction through that section of enough current to energize operating coil 66 of the sensitive relay 64. This causes the attraction of armature 72 and maintains it in engagement with stationary contact 70. No energizing circuit is at this time completed for the energizing coil 120 of the power relay since this circuit is open at contact 68. The armature 132 of the power relay is, therefore, in its spring-biased position or upward engaging stationary contact 128 to complete an obvious energizing circuit to the upper beam filaments and the lights are on high beam.

If a car now approaches and light from its headlights falls on the photo-multiplier tube 6, current in conductor 20 begins to increase. This current flow through the biasing resistors 86 and 88 reduces the voltage on control grid 60. When this flow has increased to a point Where the voltage on control grid 60 has been reduced sufficiently to cut oif current flow through the first section of the tube to deenergize coil 66, then armature 72 of the sensitive relay 64 will be released. It drops back to engage stationary contact 68 which completes the following energizing circuit for power relay coil 120. This circuit is from the battery B through control switch 1, conductors 106 and 121, through co-il 120, conductor 118, movable switch arm 116, contact 114, conductor 112, junction block 50, conductor 110, contact 68, armature 72, to ground. When this occurs, coil 120 attracts its armature 132, moving it away from engagement with stationary contact 128 and into engagement with stationary contact 130. This then deenergizes the filaments for the upper beam and energizes those for the lower beam.

At the same time that an energizing circuit is completed fior power relay coil 120, a circuit has been broken through biasing resistor 88 to change the sensitivity of the amplifier, the grid bias at this point being produced entirely by resistance 86 and the set will be much more sensitive during this portion of the cycle of operation than it was previously. In other words, a much smaller amount of light falling on the photomultiplier tube 6 will be required to keep the tube cut oif sufiiciently to maintain the sensitive relay deenergized than was initially required to deenergize it. The purpose for this change in sensitivity is to compensate for relatively large changes in incident light intensity. When a vehicle is being operated with an automatic headlight dimmer system and light intensity on the photoelectric equipment reaches a level to cause switching to the low beam, the approaching vehicle which produces the incident light will, in courtesy, usually dim its headlamps. Thus, the amount of incident light is reduced by a considerable amount at a very short time after it has caused a switching of the operated vehioles headlamps. If no change in sensitivity were provided as soon as the oncoming vehicle dimmed its lights, the system would cause a switching back to high beam when the incident light decreased. In the present instance, for example, a ratio of perhaps ten to one is incorporated. In other words, the set is ten times as sensitive after it has switched to low beam from that during high beam operation. Thus, one-tenth of the light required to cause it to switch to low beam would be necessary to maintain it in that condition. In the present design the value of the resistor 86 determines the sensitivity of the amplifier system when the device is on low beam. The amount of resistance 88 in circuit with resistor 86 during high beam operation determines the point at which the system will switch to low beam and this, of course, is variable and may be adjusted. By designing the proper amount of resistance 86 into the circuit to give the desired sensitivity when the set is on low beam, maximum efiiciency is obtained.

If the system switches automatically to low beam due to an approaching vehioles headlamps and the approaching vehcile refuses to dim its lamps, an override switch 138 is provided. The operation of this switch completes a separate energizing circuit for the sensitive relay coil 66 through the second section of the tube 62 and thus energizes coil 66 under any considerations of incident light. This pulls the armature 72 to the left breaking the energizing circuit for the operating coil 120 and the lights switch back to upper beam. This auxiliary foot switch is usually a spring-biased one and, when the operator releases it, opens to return to automatic operation.

We claim:

1. In an electrical circuit, a voltage source having one terminal connected to ground, current regulating means whose resistance increases with temperature and having one terminal connected to the other terminal of said source, a regulated power line connected to the other terminal of said current regulating means, a temperature insensitive load connected between said regulated line and ground, and a resistance whose value increases with temperature rise connected between the regulated power line and ground to compensate for changes in resistance of the current regulating means and thereby minimizing voltage surges on the regulated line.

2. In a light sensitive control system, a photosensitive device, a control device, a thermionic amplifying device having an input circuit connected to the photosensitive device for control thereby and having an output circuit connected with the control device, a power supply including a low direct voltage source, a current interrupter, a transformer with a primary winding connected across the source through the interrupter and a secondary winding connected across the photo-sensitive device, a ballast tube having a positive temperature coeificient connected serially between the interrupter and the primary winding, said thermionic device having a heater filament with a positive temperature coeflicient connected across the primary winding whereby the initial voltage across the primary Winding is limited by the resistance of the heater filament to avoid excessive voltage on the photosensitive device before the ballast tube is warmed up.

3. In a light sensitive control system, a photomultiplier tube, a relay, a thermionic amplifying tube having an input circuit connected to the photomultiplier tube and having an output circuit connected to the relay, a power supply including a low direct voltage source having one terminal connected to ground, a current interrupter, a. transformer with a primary winding connected across the source through the interrupter and having a secondary winding for energizing the photomultiplier tube, a potentiometer resistor connected across the secondary winding and having a movable contact connected to ground, said photomultiplier tube being connected across one terminal of the potentiometer and ground, a ballast tube having a positive temperature coefiicient and connected serially between the interrupter and the primary winding, said thermionic device having a heater filament with a positive temperature coefficient and connected across the primary winding whereby the initial voltage across the primary winding is limited by the resistance of the heater filament to avoid excessive voltage on the photomultiplier tube before the ballast tube is warmed up.

References Cited in the file of this patent UNITED STATES PATENTS 772,096 Hallberg Oct. 11, 1904 1,916,072 Rankin June 27, 1933 1,939,435 Cockrell Dec. 12, 1933 2,014,786 Shepard Sept. 17, 1935 2,082,497 Howe June 1, 1937 2,086,910 Hansell July 13, 1937 2,528,446 McConnell Oct. 31, 1950 2,533,286 Schmitt Dec. 12, 1950 2,560,748 Silva July 17, 1951 2,598,420 Onksen May 27, 1952 2,615,079 Pardue Oct. 21, 1952 2,685,664 Visconti Aug. 3, 1954 2,682,624 Atkins June 29, 1954 2,742,592 Miller Apr. 17, 1956 2,754,452 Onksen July 10, 1956 2,760,114 Palge Aug. 21, 1956 2,763,809 Radin Sept. 18, 1956 2,767,347 Miller Oct. 16, 1956 2,830,192 Atkins Apr. 8, 1958 

